Introduction
Despite what Dell's website states, the Inspiron 8600 will work fine on Windows 7 given it has enough hard drive space and RAM. This documentation was written for an Inspiron 8600 with Nvidia GeForce FX Go5200 graphics, 1.5 GB RAM, and Pentium M 1.7 GHz, installing Windows 7 Professional x86 to an empty, unformatted hard drive. Your mileage might vary depending on your system configuration. All processors available for the Inspiron 8600 support Windows 7, but some are faster than others; I recommend a Pentium M at 1.4 GHz or higher. Upgrades are discussed in more detail in the "Upgrades" section towards the end of this tutorial. Information here may also be applicable to Windows Vista, as the environment is similar.

Let me preface this by saying that after installation, the computer may be in a high-load state for several hours -- you won't be able to use the computer at its full potential until it finishes what it is doing. This is related to Windows Update, as far as I can tell; let the laptop run in a cool environment, connected to the Internet, and leave it overnight to do its thing. Ventilation is important; ensure the heatsinks (there is a small one to the left of the VGA port; don't forget about it) and vents are free of dust (canned/compressed air can blast out dust with ease; I highly suggest doing this with all computers every few months) and are not physically obstructed when you let it run.

But what about Windows 10?
Along with Windows 8, Windows 10 is not compatible with the Inspiron 8600, and it never will be. The processor does not support instructions required by Windows 8 and later, and thus cannot be upgraded past Windows 7.

Installation
After you have backed up your data and verified that you meet the following base requirements for a usable Windows 7 installation, you're ready to begin installation.
Base requirements:

32-bit Windows 7 (64-bit operating systems and programs are not compatible with the Pentium M)

40 GB free hard drive space

1 GB physical memory

Working optical drive supporting DVD-ROM, if installing from DVD

Insert the Windows 7 x86 DVD, and reboot the computer to boot from DVD. Select "Install Now" to continue to the partition selection screen. By default, Windows installation moves existing files to a Windows.old folder, preserving data (but not programs) at the expense of disk space. To permanently erase all data on the drive, press "Drive options (advanced)", then "Format". Press "Next" to begin installing Windows onto the selected partition. Follow the on-screen instructions after installation approaches completion (after about 30 minutes to an hour after beginning installation), and you should arrive at a Windows 7 desktop.

Drivers
When you arrive at the desktop, you will notice that many drivers are missing. Windows Update will not find drivers for most of these devices.

Audio
The audio device is a Realtek AC'97 chip, and the driver can be found on Realtek's website here. Download the file titled "Vista/Win7 (32/64 bits) Driver only (ZIP file)". Extract the files to a temporary directory (they can be deleted after installation), and run setup.exe as Administrator. Follow the on-screen instructions, and audio will be enabled after installation completes.

Network
The Inspiron 8600 has integrated Broadcom 440x ethernet and the option of Wi-Fi connectivity. Windows 7 includes drivers for the Broadcom ethernet; it will work as soon as Windows is installed, and the remainder of the drivers can be downloaded on the same computer because of this. There are a few different stock wireless cards that can be found in an Inspiron 8600: Intel 2915ABG, Intel PRO/2200BG, or Dell Wireless 1400 or 1300.

For Dell Wireless 1400/1300: Users report that this driver works when run in Compatibility Mode for Windows XP (right-click R143355.exe, select Properties, go to the Compatibility tab, check the box for "Run in compatibility mode for...", select Windows XP with the highest available SP number). Windows can manage the network card in order to use the built-in wireless network management; open the Dell Wireless utility, and uncheck the checkbox for "Let this tool manage my wireless connection". Furthermore, use MSCONFIG to disable the Dell Wireless programs from the Startup tab, to further reduce the memory footprint of unnecessary background programs.

Video
This is where things can get a bit tricky, as there are several different variations of the graphics card with different driver availabilities.

Run the installer. The driver will not install, as your computer does not actually contain a GeForce FX 5200.

Go to Control Panel, then Device Manager. Under Display Adapters, find either the Standard VGA Graphics Adapter or any installed display driver. Double-click it, go to the Driver tab, and select "Update Driver...". Select "Browse my computer manually for drivers". Windows will only suggest the Standard VGA Graphics Adapter, so you must click "Have Disk", and press "Browse" to manually load an INF file. Assuming you used the default installation directory, this INF file can be found at C:\NVIDIA\WinVista\96.85\nv_disp.inf. Select this file as the INF file to use, and you will be presented with a large list of graphics adapters. About two-thirds down the list, find the "GeForce FX 5200" driver (NOT a variation of this card), and press "Next". Windows will warn you that the driver may not be compatible with your computer; ignore this warning and press "Yes". The driver will install, and Windows will ask to restart your computer; do so.

The GeForce FX 5200 driver has issues with Windows Aero effects, and my Inspiron 8600 had issues with Aero transparency and UAC screen dimming. The last step in the above list disables Aero transparency to prevent issues. I have not tested this driver with gaming environments, and do know that Minecraft > 1.7.2 will not run; for gaming, use the Windows XP drivers. The card supports DirectX 9.

I do not know much about the Nvidia GeForce Go5650 or GeForce4 4200 Go options, but the general-case solution for these is to install the Windows XP drivers in compatibility mode. The GeForce Go5650 might work with the GeForce 5600 drivers using the above method, but I have not tested it and do not have the means to do so.

Upgrades
As mentioned above, you'll want the latest BIOS version before upgrading anything, as newer BIOSes have broader parts support.

RAM
The latest BIOS versions support PC-2700 DDR memory with capacities up to 2 GB. For Windows 7 to perform well with programs, 1 GB memory is needed. A 2 GB kit can be found on Amazon for about $27. The Inspiron 8600 will not recognize capacities above 2 GB, so don't waste your money.